Unoriented polypropylene molding

ABSTRACT

An unoriented polypropylene-based film or sheet possessing excellent impact resistance at low temperature, transparency, heat resistance at low temperature and excellent tear strength and/or stress whitening resistance. A molding material which comprises a polypropylene-based resin material comprising 40 to 80% by weight of crystalline polypropylene and 60 to 20% by weight of propylene-α-olefin copolymer containing 20 to 80% by weight of propylene polymerization units, the propylene-α-olefin copolymer dispersed as particles in the crystalline polypropylene, is unoriently molded to afford a film-shaped or sheet-shaped molding, wherein the particle diameter have an aspect ratio (L/D) of mean dispersed particle length (L) to mean dispersed particle diameter along the thickness of the molding (D) of 30 or more in a cross section of the molding along the MD direction, and the mean dispersed particle diameter of 0.3 μm or less.

TECHNICAL FIELD

The present invention relates to a film-shaped or sheet-shapedunoriented molding formed from a molding material comprising apolypropylene-based resin material. More precisely, it relates to anunoriented polypropylene-based film having excellent transparency,impact resistance at low temperature and heat resistance as well asexcellent tear resistance, or to an unoriented polypropylene-based sheethaving excellent transparency, impact resistance at low temperature andheat resistance as well as excellent stress whitening resistance againstan impact such as a drop or a hit.

BACKGROUND ART

Films or sheets of polypropylene-based resins have such characteristicsthat those are inexpensive and have excellent chemical resistance, oilresistance, mechanical strength, transparency, and heat resistance.Accordingly, those are widely utilized as materials for packaging food,textiles, etc. and as food containers, industrial material parts orstationery such as files.

The conventional unoriented polypropylene-based resin films or sheetshave excellent heat resistance, however, they are poor in impactresistance at low temperature and tear strength if a compositioncontaining a homopolymer of a propylene is used for the unorientedpolypropylene-based resin films or sheets. On the other hand, if acopolymer composition containing a propylene-α-olefin random copolymeris used therefor, though they have excellent transparency, their heatresistance and impact resistance at low temperature are poor. Inaddition, in case where a composition of a block copolymer consisting ofa propylene homopolymer and a propylene-α-olefin copolymer is usedtherefor, impact resistance at low temperature is excellent, but thereare such defects that transparency is low, tear strength is poor,whitening due to impacts such as a drop or a hit is remarkable.

Therefore, in the conventional unoriented films or sheets using apolypropylene, it has not been easy to obtain ones satisfying all oftransparency, impact resistance at low temperature and heat resistance,while possessing excellent tear strength and/or stress whiteningresistance against impact (property that is not liable to be white dueto impact).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an unorientedpolypropylene-based film or sheet having excellent transparency and heatresistance as well as excellent tear strength and/or stress whiteningresistance, without deteriorating impact resistance at low temperature.

The present inventors earnestly conducted studies in order to achievethe foregoing object. As a result, they found that, in an unorientedmolding composed of a polypropylene-based material comprising apropylene-α-olefin copolymer is dispersed as particles in crystallinepolypropylene, transparency and heat resistance are improved without thedeterioration of impact resistance at low temperature, and in addition,tear strength and stress whitening resistance can also be improved bycontrolling the copolymer particles so as to have a specific dispersionstate in a cross-section along an MD direction of the molding. Thus,they have accomplished the present invention.

That is, the present invention provides an unorientedpolypropylene-based molding which is a film-shaped or sheet-shapedmolding formed from a molding material comprising a polypropylene-basedresin material, the material comprising 40 to 80% by weight ofcrystalline polypropylene and 60 to 20% by weight of propylene-α-olefincopolymer containing 20 to 80% by weight of propylene polymerizationunits, the propylene-α-olefin copolymer dispersed as particles in thecrystalline polypropylene, wherein the particles of the copolymer havean aspect ratio (L/D) of mean dispersed particle length (L) to meandispersed particle diameter along the thickness of the molding (D) of 30or more in a cross section of the molding along the MD direction, andthe mean dispersed particle diameter of 0.3 μm or less.

The unoriented molding having the above characteristics in form ispreferably that a ratio of MFR of the crystalline polypropylene to thatof the propylene-α-olefin copolymer (MFR of the crystallinepolypropylene/MFR of the propylene-α-olefin copolymer) is 10 or less.

The above-mentioned unoriented polypropylene-based molding is preferablyan unoriented film having a thickness of 10 to less than 100 4 μm.

The above-mentioned unoriented polypropylene-based molding is preferablya sheet having a thickness of 0.1 to 4 mm.

The unoriented molding of the present invention comprises the elongatedcopolymer particles dispersed in a matrix of the crystallinepolypropylene in such a manner the particles should have an aspect ratiohigher than a certain level, and an unoriented film of sheets havingsuch a dispersion state has been made by the present invention for thefirst time.

According to the present invention, an unoriented film having excellentimpact resistance at low temperature, transparency, heat resistance andtear strength can be obtained thanks to such characteristics in form.

Further, according to the present invention, a sheet having excellentimpact resistance at low temperature, transparency, heat resistance andstress whitening resistance can be obtained thanks to suchcharacteristics in form.

The unoriented film of the present invention is useful as a film forpackage, in particular, as a film for food package (for example, forpackaging retort foods or for packaging frozen foods) that requirestransparency as well as impact resistance at low temperature, heatresistance and tear strength.

Further, the sheet of the present invention is useful as sheets forstationary such as files, or industrial material parts, in particular,as sheets for food packaging containers, sheets for industrial materialparts or the like (for example, sheets for cosmetic papers, sheets forcivil engineering) that particularly requires transparency as well asstress whitening resistance and impact resistance at low temperature.

Preferred embodiments of the present invention will be explainedhereinafter.

(1) Polypropylene-based Resin Material of the Present Invention

The molding material for forming the unoriented molding of the presentinvention comprises a polypropylene-based resin material that consistsof crystalline polypropylene and propylene-α-olefin copolymer, thecopolymer being dispersed as particles in the crystalline polypropylene(the copolymer is dispersed as domains in a matrix of the crystallinepolypropylene).

(i) Crystalline Polypropylene

The crystalline polypropylene used for the present invention is acrystalline polymer comprising principally of propylene units, andpreferably comprises 90% by weight or more of the propylene units basedon the whole polymer. Specifically, it may be a homopolymer ofpropylene, or it may be a random copolymer comprising 90% by weight ormore of propylene units and less than 10% by weight of α-olefin. When itis a copolymer, the α-olefin may include ethylene, 1-butene, 1-pentene,1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene,3-methyl-1-pentene, and the like. It is preferable in view of theproduction cost to use a propylene homopolymer or propylene-ethylenerandom copolymer having a propylene unit content of 90% by weight ormore.

The melt flow rate (abbreviated as “MFR” hereinafter) of the crystallinepolypropylene is preferably in the range of 0.1-50 g/10 minutes in viewof the stability upon film-forming.

(ii) Propylene-α-olefin Copolymer

The propylene-α-olefin copolymer used for the present invention is arandom copolymer of propylene and an α-olefin other than propylene. Thecontent of propylene unit is preferably in the range of 20-80% byweight, more preferably 20-75% by weight, particularly preferably 20-70%by weight based on the whole copolymer. When the content of propyleneunit exceeds 80%, the desired dispersed state of the copolymer particles(referred to as “copolymer domains” hereinafter) in the matrix ofcrystalline polypropylene may not be obtained, and it is not practicallypreferable in the point that improvement effect of impact resistance atlow temperature and tear strength, which is the purpose of the presentinvention, are not sufficiently obtained. On the other hand, when it isless than 20% by weight, the copolymer domains purposed in the presentinvention are difficult to be formed, and it is not practicallypreferable in the point that impact resistance at low temperature andtransparency are not sufficiently exhibited.

As the α-olefin other than propylene, ethylene, 1-butene, 1-pentene,1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene,3-methyl-1-pentene and the like can be mentioned. Among these, apropylene-ethylene copolymer containing ethylene as the α-olefin ispreferably used because it is beneficial to the production cost.

While MFR of the propylene-α-olefin copolymer used for the presentinvention is not particularly limited, it is preferably in the range of0.1-20 g/10 minutes.

More preferably, MFR of the propylene-α-olefin copolymer is preferablyselected so that its ratio to MFR of the crystalline polypropylene (MFRof the crystalline polypropylene/MFR of the propylene-α-olefincopolymer, referred to as “MFR ratio” hereinafter) should be 10 or less,more preferably in a range of 0.1-5.

(iii) Polypropylene-based Resin Material

In the polypropylene-based resin material of the present invention, thecontent of the crystalline polypropylene is 40-80% by weight, preferably50-80% by weight, and the content of the propylene-α-olefin copolymer is60-20% by weight, preferably 50-20% by weight based on the wholepolypropylene-based resin material. When the ratio of the copolymer isless than 20% by weight, sufficient impact resistance at low temperatureand tear strength cannot be obtained. When it exceeds 60% by weight, therigidity of the film is markedly decreased, and it is not preferred forpractical use.

The production method of the polypropylene-based resin material is notparticularly limited, and it can be obtained by any kind of method. Forexample, it can be obtained by mixing crystalline polypropylene andpropylene-α-olefin copolymer, which were polymerized separately, throughmelt-kneading or the like. Alternatively, it can be obtained bycontinuously polymerizing crystalline polypropylene andpropylene-α-olefin copolymer by multi-step polymerization.

Specifically, a method based on melt-kneading of propylene-α-olefincopolymer polymerized by using a Ziegler-Natta catalyst such as atitanium-supported catalyst or a commercially availableethylene-propylene rubber and crystalline polypropylene can beexemplified. As the method for continuously polymerizing crystallinepolypropylene and propylene-α-olefin copolymer by multi-steppolymerization, for example, a method comprising producing propylenehomopolymer in the first step, and producing propylene-α-olefincopolymer in the second step by utilizing a plurality of polymerizationreactions can be exemplified. This continuous polymerization method ispreferred, because it can be performed at a lower cost compared with theaforementioned melt-mixing method, and can produce a polypropylene-basedresin material where the propylene-α-olefin copolymer is uniformlydispersed in the crystalline polypropylene, and it is suitable forstably realizing the desired quality (good transparency and tearstrength).

As the polypropylene-based resin material of the present invention,particularly preferred are those produced by the aforementionedcontinuous polymerization method so that the resulting material shouldhave the MFR ratio of the crystalline polypropylene and thepropylene-α-olefin copolymer (MFR of the crystalline polypropylene/MFRof the propylene-α-olefin copolymer) of 10 or less, more preferably inthe range of 0.1-5. By selecting the MFR ratio in the aforementionedrange, the propylene-α-olefin copolymer can be uniformly and finelydispersed in the crystalline polypropylene, and the copolymer particlescan have elongated form with an aspect ratio higher than a certainlevel. This provide a polypropylene-based unoriented molding (film orsheet) having good transparency and excellent tear strength and/orstress whitening resistance.

Specifically, polypropylene-based resin materials having such an MFRratio can be produced by the methods mentioned in Japanese PatentUnexamined Publication Nos. 6-239918, 8-27238, and the like.

The MFR ratio can usually be calculated by measuring the MFR of thecrystalline polypropylene and the propylene-α-olefin copolymerrespectively, but when the polypropylene-based resin material iscontinuously produced by the multi-step polymerization method (thecrystalline polypropylene is polymerized first, and then thepropylene-α-olefin copolymer is polymerized), the MFR of thepropylene-α-olefin copolymer cannot be directly measured. In such acase, the MFR of the propylene-α-olefin copolymer can be obtained fromthe MFR of the crystalline polypropylene, which can be directlymeasured, the MFR of the obtained polypropylene-based resin material,and the content of the propylene-α-olefin copolymer in thepolypropylene-based resin material according to the following equation:${\log \left( {MFR}_{RC} \right)} = \frac{{\log \left( {MFR}_{whole} \right)} - {\left( {1 - {W_{RC}/100}} \right){\log \left( {MFR}_{PP} \right)}}}{W_{RC}/100}$

MFR_(RC): MFR of propylene-α-olefin copolymer

MFR_(whole): MFR of polypropylene-based resin material

MFR_(pp): MFR of crystalline polypropylene

W_(RC): Content of propylene-α-olefin copolymer in polypropylene-basedresin material

(2) Molding Material of the Present Invention

While the molding material of the present invention is mainly composedof the aforementioned polypropylene-based resin material, it may furthercontain additives conventionally used for polyolefine-based filmmaterials, for example, antioxidant, neutralizer, light stabilizer,inorganic filler, lubricant, anti-blocking agents, antistatic agent andthe like.

Examples of the antioxidant include, for example, phenolic antioxidantssuch astetrakis[methylene-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane,2,6-di-t-butyl-4-methylphenol,n-octadecyl-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate, andtris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate; phosphorus-containingantioxidants such as tris(2,4-di-t-butylphenyl) phosphite,tris(nonylphenyl) phosphite, distearylpentaerythritol diphosphite, andtetrakis(2,4-di-t-butylphenyl)-4,4′-biphenylenediphosphonite, and thelike.

Examples of the neutralizer include, for example, salts of higher fattyacid such as calcium stearate. Examples of the inorganic filler and theanti-blocking agents include, for example, calcium carbonate, silica,hydrotalcite, zeolite, aluminum silicate, magnesium silicate and thelike. Examples of the lubricant include, for example, higher fatty acidamides such as stearic acid amide and the like; and examples of theantistatic agents include, for example, fatty acid esters such asglycerin monostearate and the like.

While the amounts of these additives may be suitably selected dependingon the intended use of the molding (film or sheet), they are preferablyused in an amount of about 0.001-5% by weight based on the whole moldingmaterial in general. Further, in the sheet, it is preferable that thecontents of the inorganic fillers are 0.001-75% by weight, the contentsof synthetic rubbers are 0.5-60% by weight and the contents of otheradditives are generally about 0.001-5% by weight.

The method for mixing the polypropylene-based resin material and theaforementioned additives is not particularly limited, and it can beperformed, for example, by mixing methods utilizing conventional mixingapparatuses including mixers provided with high-speed agitators such asHenschel mixer (trade name), ribbon blender and tumbler mixer and thelike (dry blend), as well as methods for pelletization utilizing aconventional single-screw extruder, twin-screw extruder and the like.

(3) Molding of the Molding Material

Of the moldings of the present invention, the unoriented film isobtained by extrusion molding the above-mentioned molding material withthe conventional method. For example, it can be produced by T-die castmethod, water cooling inflation method or the like.

The sheet of the present invention can be produced by the knownextrusion molding, calender molding, cast molding or the like. Of theconventional molding methods, the extrusion molding is preferable in thepoint of productivity. Specifically, the T-die method using an apparatus(T-die sheet molding machine) having steps of extruder, T-die, polishingroll (cooling roll), guide roll, take-up roll, trimming cutter, masking,constant-length cutter, stacker and the like is further preferable.

The resin temperature in molding the sheet is preferably 180-300° C. Ifthe resin temperature is 180° C. or higher, the polypropylene-basedresin material is sufficiently melted, and the sheet surface does notshow a rough-skinned state but shows good appearance. Further, if theresin temperature is 300° C. or lower, heat deterioration of thepolypropylene-based resin material due to heat is hardly occurred, melttension of the sheet can be maintained and thus good moldability isobtained.

The cooling roll temperature in molding the sheet is preferably 5-80° C.If the cooling roll temperature is 5° C. or higher, the cooling rolldoes not cause dew condensation, and as a result, spot-like pattern isnot formed on the sheet surface and good surface appearance can beobtained. Further, if the cooling roll temperature is 80° C. or lower,the sheet can sufficiently be cooled, and as a result, a linear patternformed in unwinding a rolled sheet is not formed and good surfaceappearance can be obtained.

The molding speed of the sheet is preferably about 0.1-100 m/min. If themolding speed is 0.1 m/min or more, a sheet having uniform thickness canbe obtained and fraction defective is small. If the molding speed is 100m/min or less, the sheet is sufficiently cooled, and as a result, alinear pattern formed in unwinding a rolled sheet is not formed and goodsurface appearance can be obtained.

(4) Unoriented Polypropylene-based Molding

In the film-shaped or sheet-shaped unoriented polypropylene-basedmolding of the present invention, the propylene-α-olefin copolymerdomains dispersed as particles in the crystalline polypropylene have amean dispersed particle diameter along the film thickness direction of0.3 μm or less, preferably 0.2 μm or less in a cross section along theMD direction. When the mean dispersed particle diameter is more than 0.3μm, the transparency is degraded. On the other hand, the lower limit ofthe mean dispersed particle diameter is not particularly defined, and itmay be however small so long as the copolymer domains can be observed.However, the mean dispersed particle diameter is preferably not lessthan 0.02 μm.

The molding of the present invention is also characterized by the aspectratio (L/D) of 30 or more, preferably 50 or more, as for the ratio ofthe mean dispersed particle length (L) to the aforementioned meandispersed particle diameter (D) of the copolymer domains in a crosssection along the MD direction.

The relationship between the mean dispersed length (L) and the meandispersed particle diameter (D) is schematically shown in FIG. 1(a) and(b). The mean dispersed particle diameter (D) in a cross section alongthe MD direction is the average of the particle diameter (breadth) ofthe dispersed particles along the molding thickness direction when thecross section of the film or the sheet along the MD direction isobserved from the perpendicular direction to the MD direction (MDobservation: edge view). The mean dispersed length (L) is the average ofthe length of the dispersed particles in the aforementioned MDobservation.

According to the present invention, such fine and elongated copolymerdomains are uniformly dispersed in the matrix. This provides anunoriented film or sheet having excellent tear strength and/or stresswhitening resistance as well as excellent transparency. The aspect ratioof less than 30 is not preferred, because the film or the sheet withsuch an aspect ratio may degrade the tear strength and/or stresswhitening resistance and transparency also be lowers.

Although the upper limit of the aspect ratio is not particularlylimited, it is preferably about 500 when a length of one copolymerparticle is regarded as the particle diameter along the MD direction ofthe copolymer domain. However, there is the case that the copolymerparticles may be fused and mutually connect along the MD direction and aplurality of copolymer particles are united to form a single copolymerdomain. In this case, when the multiple fused copolymer particles isconsidered as one copolymer domain, the particle diameter along the MDdirection may be several times as large as the length of one copolymerparticle. The maximum aspect ratio of such a copolymer domain in such acase may be several times that of one copolymer domain composed of onecopolymer particle as mentioned above, specifically 10 to 50 times, andthe aspect ratio may reach as high as around 300 to 1,500.

When a cross section along the TD direction of the molding of thepresent invention is observed from the perpendicular direction to the TDdirection (TD observation: end view), the copolymer domains may be aflat shape in molding. In such a case, the aspect ratio (L′/D) of themean dispersed length (L′) to the mean dispersed particle diameter (D)along the thickness direction of the molding in the cross section alongthe TD direction is preferably, while it is not particularly limited,about 1 to about 10. The TD observation is schematically shown in FIG.1(c).

According to the present invention, it was found for the first time thata film-shaped or sheet-shaped unoriented molding containing thecopolymer domains which exhibited such a fine mean dispersed particlediameter and such an aspect ratio as described above has excellenttransparency, impact resistance at low temperature and heat resistanceas well as excellent tear strength and stress whitening resistance.Therefore, the molding may be a film or sheet obtained by any kind ofmethod so long as the film or sheet satisfies the requirementsconcerning the particle diameter of the copolymer domains. Specifically,the unoriented film or sheet satisfying the requirements can be obtainedby extrusion molding a polypropylene-based resin material produced bythe above-mentioned continuous polymerization method.

The thickness of the unoriented polypropylene-based film of the presentinvention is preferably 10 μm to less than 100 μm, more preferably 15 to70 μm, in view of the moldability of the film.

The thickness of the unoriented polypropylene-based sheet of the presentinvention is preferably 0.07 to 4 mm, more preferably 0.1 to 4 mm, andparticularly preferably 0.1 to 3 mm, in view of the moldability of thesheet.

The unoriented polypropylene-based film of the present invention hasexcellent cold resistance at low temperature as well as excellent tearstrength, and also maintains transparency and heat resistance.Therefore, it can be preferably used as, for example, materials forpackaging vegetables, for packaging breads, for packaging frozen food,or the like.

The unoriented polypropylene-based sheet of the present invention hasexcellent cold resistance at low temperature (impact resistance at lowtemperature) as well as stress whitening resistance and transparency,and maintains heat resistance. Therefore, it can be preferably used asstationary such as files and industrial materials such as food packagingmaterial or cosmetic paper.

The film-shaped or sheet-shaped unoriented polypropylene-based moldingof the present invention can also be used for a multilayer film or amultilayer sheet comprising two or more layers, which can be prepared bylaminating one or more films or sheets made of other resins on one orboth sides of the molding of the present invention. The other resinsused in such a case are not particularly limited, and various resins canbe used depending on the purpose. For example, when a layer composed ofheat adhesive resin such as propylene-α-olefin copolymer having a lowmelting point is provided on the unoriented molding of the presentinvention, it can be used as various packaging materials. An in-linelaminating method, a co-extrusion method and the like, which areperformed during the production stage of a film or sheet, a drylaminating method or the like in which lamination is performed afterproduction of a film or sheet, can be applied to the method forproducing such a multilayer film or multilayer sheet.

The unoriented polypropylene-based molding or multilayer film ormultilayer sheet of the present invention can be subjected to surfacetreatment such as corona discharge treatment, flame treatment or plasmatreatment according to a general method industrially employed for thepurpose of imparting printability, lamination characteristic, metaldeposition characteristic or the like.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 includes schematic views representing the relationship betweenthe mean dispersed particle length (L) and the mean dispersed particlediameter (D) in a cross section along the MD direction. FIG. 1(a) is aperspective view of the film-shaped or sheet-shaped molding, FIG. 1(b)is a view of the MD observation representing a cross section along theMD direction, and FIG. 1(c) is a view of the TD observation representinga cross section along the TD direction.

FIG. 2 is an electron microscope photograph (magnification: ×5000) whichshows the particle state of copolymer domains along the MD direction inthe unoriented film obtained in Example 2.

FIG. 3 is an electron microscope photograph (magnification: ×5000) whichshows the particle state of copolymer domains along the TD direction inthe unoriented film obtained in Example 2.

FIG. 4 is an electron microscope photograph (magnification: ×5000) whichshows the particle state of copolymer domains along the MD direction inthe sheet obtained in Example 7.

FIG. 5 is an electron microscope photograph (magnification: ×5000) whichshows the particle state of copolymer domains along the TD direction inthe sheet obtained in Example 7.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be further explained more specificallyhereinafter with reference to the following examples, but the presentinvention is not limited by these examples.

EXAMPLES 1-5 AND COMPARATIVE EXAMPLES 1-3

(1) Production of Molding Materials

0.03% by weight oftetrakis[methylene-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane asa phenolic antioxidant, 0.08% by weight oftris(2,4-di-t-butylphenyl)phosphite as a phosphorus-containingantioxidant, 0.1% by weight of calcium stearate as a neutralizer, 0.2%by weight of silica as an anti-blocking agent and 0.1% by weight ofoleic acid amide as a lubricant include, based on the whole weight ofthe molding materials, were blended with polypropylene-based resinmaterials as shown in Table 1. These were blended by a Henschel mixer(trade name), melt-kneaded and pelletized by a single-screw extruder(aperture of 40 mm diameter) to obtain a molding material.

The polypropylene-based resin materials used in these examples wereobtained by the continuous polymerization method where crystallinepolypropylene was polymerized in the first step, and propylene-α-olefincopolymer (propylene-ethylene copolymer) was polymerized in the secondstep.

The values of MFR of the polypropylene-based resin materials and that ofthe crystalline polypropylenes, both shown in Table 1, were determinedaccording to JIS-K-7210 under the conditions of test temperature of 230°C. and test load of 21.18 N.

(2) Production of Unoriented Films

The pellets obtained in the above pelletization were melt-extruded at230° C. using a single layer extruder (aperture of 65 mm diameter)equipped with a T-die and cooled and solidified by an air chamber andcooling roller having a surface temperature of 30° C. to obtain anunoriented film having a thickness of 25 4m.

(3) Evaluation

Various physical property values of the obtained unoriented film, i.e.,mean dispersed particle diameter and aspect ratio in the cross sectionalong MD direction of a copolymer domain in the film, a transparency(haze) of the film, a impact resistance, a heat resistance, and a tearstrength along the TD direction, are shown in Table 1. Evaluationmethods of these physical property values are as follows.

(a) Dispersed Particle Diameter and Aspect Ratio in Cross Section AlongMD Direction of Copolymer Domains

An unoriented film was cut along the parallel directions to the MDdirection, dyed in vapor phase with a ruthenium compound (RuO₄) for 48hours, and then cut into pieces having a thickness of about 100 nm witha diamond knife using an ultramicrotome to prepare ultrathin sections.The obtained ultrathin sections were observed by using a transmissionelectron microscope (tradename: JEOLJEM 100CX) at a magnification of5,000, each of mean dispersed particle diameter of the copolymer domainsalong the MD direction and mean dispersed particle length along the TDwas obtained through statistical processing of the electron microscopephotograph, and aspect ratio was calculated from them.

(b) Tear Strength (TD direction)

Elemendorf tear strength of an unoriented film was measured according toASTM D-1922. The larger value means that the film is hardly to tear.

(c) Haze

Haze of an unoriented film (unit: %) was measured according toASTM-D-1003, and used as a parameter of transparency. A smaller valueindicates better transparency.

(d) Impact Resistance

An unoriented film was leaved in a thermostat set to a predeterminedtemperature for 15 minutes, and a shock strength was measured accordingto ASTM-D-781. The temperature at which the strength became 0.5 J orless was used as an index of the impact resistance at low temperature. Alower temperature means that the shock residence of the film is better.

(e) Heat Resistance

A rectangular sample of 10×100 mm, cut from an unoriented film, wasdipped in a silicone oil bath set to a predetermined temperature andleaved therein for 10 minutes. A length along longitudinal direction ofthe sample was measured and a temperature at which a value expressed inpercentage of the shrunk length to an initial length exceeds 2% was usedas an index of the heat resistance. A higher temperature means that theheat resistance of the film is better.

TABLE 1 Comparative Example Example 1 2 3 4 5 1 2 3 (1)Polypropylene-based resin Crystalline polypropylene 70.8   75 62.2 71.1   67 70.8  70.3  82.3  content (wt %) Propylene content in 100 100100  99.7*¹ 100 100 100 100 crystalline polypropylene (wt %) Copolymer*²content (wt %) 29.2   25 37.8  28.9   33 29.2  29.7  17.7  Propylenecontent in  66  64  67  65  63  64  82  66 copolymer (wt %) MFR ofpolypropylene-based  6 6.2 6.5  4  3 6.2 6.2 6.2 resin (g/10 min) MFR ofcrystalline 7.2 6.2 6.5 2.8  3  34 6.2 6.2 polypropylene (g/10 min) MFRratio*³ 1.7  1  1  0.26  1 82.9   1  1 (2) Various physical propertiesof film Mean dispersed particle  0.13  0.11  0.11 0.1  0.11 1.3  0.08 0.11 diameter of copolymer (μm) Aspect ratio of copolymer(L/D) >50 >50 >50 >50 >50  <2 >50 >50 Haze (%) 9.1  2 5.8 5.5 8.2 31.7 1.8 1.8 Impact resistance at low −20 −20 −20 −25 −25 −25  −5  0temperature (° C.) Heat resistance (° C.) 130 135 120 130 130 130 130140 Tear strength along TD direction  24  26  60  51  27  11  8  9(N/mm) *¹Propylene/ethylene copolymer *²Propylene/ethylene copolymer*³MFR ratio = MFR of crystalline PP/MFR of copolymer

The electron microscope photograph (magnification: ×5000) of theultrathin section, used for obtaining the mean dispersed particlediameter and the mean dispersed particle length of the copolymer domainsin a cross section along the MD direction of the unoriented filmobtained in Example 2, was shown in FIG. 2. FIG. 2 shows a photograph ofthe surface cut along the perpendicular direction to the MD direction ofthe ultrathin section. An electron microscope photograph in the casethat the ultrathin section is cut along the perpendicular direction tothe TD direction is shown in FIG. 3. FIG. 2 and FIG. 3 show electronmicroscope photographs representing particle state of the copolymerdomains in the aforementioned film along the MD and TD directions,respectively.

As seen from the results shown in Table 1, the films of Examples 1-5have excellent impact resistance at low temperature, heat resistance,and transparency and high tear strength. Moreover, as seen from FIGS. 2and 3, the unoriented film of the present invention has a elongatedcopolymer domains dispersed finely and uniformly.

On the other hand, in Comparative Example 1, the mean dispersed particlediameter of the propylene-α-olefin copolymer is too large and the aspectratio is low, so that only a film having poor transparency and low tearstrength is obtained. In Comparative Example 2, the propylene content inthe propylene-α-olefin copolymer in the polypropylene-based resinmaterial is large, and in Comparative Example 3, the proportion of thepropylene-α-olefin copolymer to the polypropylene-based resin materialis small. Therefore, in Comparative Examples 2 and 3, only films havinginsufficient impact resistance at low temperature and low tear strengthis obtained.

EXAMPLES 6-11 AND COMPARATIVE EXAMPLES 4-7

(1) Production of Molding Materials

0.03% by weight ofTetrakis[methylene-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane asa phenolic antioxidant, 0.08% by weight oftris(2,4-di-t-butylphenyl)phosphite as a phosphorus-containingantioxidant, and 0.1% by weight of calcium stearate as a neutralizer,based on the whole weight of the molding materials, were blended withpolypropylene-based resin materials as shown in Table 2. These wereblended by a Henschel mixer (trade name), melt-kneaded and pelletized bya single screw extruder (aperture of 40 mm diameter) to obtain a sheetmolding material.

The polypropylene-based resin materials used in these examples wereobtained by the continuous polymerization method where crystallinepolypropylene was polymerized in the first step, and propylene-α-olefincopolymer (propylene-ethylene copolymer) was polymerized in the secondstep.

The values of MFR of the polypropylene-based resin materials and that ofthe crystalline polypropylenes, both shown in Table 2, were determinedaccording to JIS-K-7210 under conditions of test temperature of 230° C.and test load of 21.18 N.

(2) Production of Sheets

The pellets obtained in the above pelletization were molded by a T-diemethod using a sheet molding apparatus having a T-die and a polishingroll at an extrusion temperature of 230° C., a cooling roll temperatureof 50° C. and a molding speed of 2 mm/min to obtain a sheet having athickness of 0.6 mm.

(3) Evaluation

Various physical property values of the obtained sheet, i.e., meandispersed particle diameter and aspect ratio in the cross section alongthe MD direction of a copolymer domain in the sheet, a transparency(haze) of the sheet, a impact resistance, a heat resistance and a stresswhitening resistance, are shown in Table 2. Evaluation methods of thosephysical property values are as follows.

(a) Dispersed Particle Diameter and Aspect Ratio in Cross Section Alongthe MD Direction of Copolymer Domains

A sheet was cut along at the parallel directions to the MD direction,dyed in vapor phase with a ruthenium compound (RuO₄) for 48 hours, andthen cut into pieces having a thickness of about 100 nm with a diamondknife using an ultramicrotome to prepare ultrathin sections. Theobtained ultrathin sections were observed by using a transmissionelectron microscope (trade name: JEOLJEM 100CX) at a magnification of5,000, each of mean dispersed particle diameter of the copolymer domainsalong the MD direction and mean dispersed particle lengths along the TDdirection was obtained through statistical processing of the electronmicroscope photograph, and aspect ratio was calculated from them.

(b) Haze

Haze of a sheet (unit: %) was measured according to ASTM-D-1003, andused as a parameter of transparency. A smaller value indicates bettertransparency.

(c) Heat Resistance

Vicat softening temperature was measured according to JIS-K7206, used asan index of heat resistance. A larger value indicates better heatresistance.

(d) Impact Resistance

Impact resistance in punching-out of a sheet at −20° C. was measuredaccording to ASTM-D-781.

(e) Stress Whitening Resistance

A sheet was cut into a size having a width of 10 mm and a length of 120mm, and this was used as a test piece. Both ends of this test piece werebent so as to gradually approach with each other. Bending the test piecewas continued until the curved portion of the test piece became white.The curvature at the curved portion when the curved portion started tobe white was determined, and the value of a diameter of a circlecorresponding to this curvature was used as an index of the stresswhitening resistance. A smaller value indicates better stress whiteningresistance.

TABLE 2 Example Comparative Example 6 7 8 9 10 11 4 5 6 7 (1)Polypropylene-based resin Crystalline polypropylene  68 76.9  72.2   67 67  56 75.6  85.5  66.5 85.5  content (wt %) Propylene content in 100100 100  99.7*¹ 100 100 100 98.8  100 100 crystalline polypropylene (wt%) Copolymer*² content (wt %)  32 23.1  27.8   33  33  44 24.4  14.5 33.5  14.5  Propylene content in  63  60  64  62  55  64  54  62  55  66copolymer (wt %) MFR of polypropylene-based  0.84 3.4 1.7 3.1  8 0.7 2.72.1 2.3 3.2 resin (g/10 min) MFR of crystalline 0.7  5 1.7 3.1 11.5  0.75.3 6.1 7.9 3.2 polypropylene (g/10 min) MFR ratio*³  0.57  2  1  1  3 1 17.7  1500  39.4   1 (2) Various physical properties of film Meandispersed particle  0.12  0.15  0.13  0.14  0.16  0.13  1.3 1.5 1.50.14  diameter of copolymer (μm) Aspect ratio of copolymer(L/D) >50 >50 >50 >50 >50 >50  <2  <2  <2 >50 Haze (%)  47  45  47  47 58  60  95  93  95  60 Vicat softening temperature 114 140 128 116 118105 137 156 118 154 (° C.) Impact resistance in punching  >3  >3  >3  >3 >3  >3  >3  >3  >3  <1 (−20° C.) (J) Stress Whitening resistance  <3 <3  <3  <3  <3  <3  20  25  25  15 (diameter of circle of curvature)(mm diameter) *¹Propylene/ethylene copolymer *²Propylene/ethylenecopolymer *³Ratio of MFR = MFR of crystalline PP/MFR of copolymer

An electron microscope photograph (magnification: ×5000) of theultrathin section, used for obtaining the mean dispersed particlediameter and the mean dispersed length the copolymer domains in a crosssection along the MD direction of the sheet obtained in Example 7, wasshown in FIG. 4. FIG. 4 shows a photograph of the surface cut along theperpendicular direction to the MD direction of the ultrathin section. Anelectron microscope photograph in the case that the ultrathin section iscut along the perpendicular direction to the TD direction is shown inFIG. 5. FIG. 4 and FIG. 5 show photographs representing particle stateof the copolymer domains in the aforementioned sheet along the MDdirection and the TD direction, respectively.

As seen from the results shown in Table 2, the sheets of Examples 6-11have good impact resistance at low temperature, heat resistance andtransparency, and also have excellent stress whitening resistance due tobending. Moreover, as seen from FIG. 4 and FIG. 5, the sheet of thepresent invention has a elongated copolymer domains dispersed finely anduniformly.

On the other hand, in Comparative Examples 4-6, the mean dispersedparticle diameter of the propylene-αolefin copolymer is too large andthe aspect ratio is low, so that only a film having poor transparencyand stress whitening resistance is obtained. In Comparative Example 7,the proportion of the propylene-α-olefin copolymer to thepolypropylene-based resin material is small. Therefore, in ComparativeExample 7, only a sheet having insufficient impact resistance at lowtemperature and stress whitening resistance is obtained.

INDUSTRIAL APPLICABILITY

The unoriented molding of the present invention has excellent impactresistance at low temperature, transparency and heat resistance as wellas excellent tear strength and/or stress whitening resistance.

What is claimed is:
 1. An unoriented polypropylene-based molding whichis a film-shaped or sheet-shaped molding formed from a molding materialcomprising a polypropylene-based resin material, the material comprising40 to 80% by weight of crystalline polypropylene and 60 to 20% by weightof propylene-α-olefin copolymer containing 20 to 80% by weight ofpropylene units, the propylene-α-olefin copolymer dispersed as particlesin the crystalline polypropylene, wherein the particles of the copolymerhave an aspect ratio (L/D) of mean dispersed particle length (L) to meandispersed particle diameter along the thickness of the molding (D) of 30or more in a cross section of the molding along the MD direction, andthe mean dispersed particle diameter of 0.3 μm or less.
 2. Theunoriented polypropylene-based molding of claim 1, wherein a ratio ofMFR of the crystalline polypropylene to that of the propylene-α-olefincopolymer (MFR of the crystalline polypropylene/MFR of thepropylene-α-olefin copolymer) is 10 or less.
 3. The unorientedpolypropylene-based molding of claim 1 or 2, wherein the unorientedmolding is an unoriented film having a thickness of 10 to less than 100μm.
 4. The unoriented polypropylene-based molding of claim 1 or 2,wherein the unoriented molding is a sheet having a thickness of 0.1 to 4mm.
 5. The unoriented polypropylene-based molding of claim 1 or 2,wherein the polypropylene-based material is produced by continuouspolymerization method.